Human Influences and Decreasing Synchrony between Meteorological and Hydrological Droughts in Wisconsin Since the 1980s

Hydrological droughts are important for agriculture and other human activities such as navigation and groundwater pumping, so it is necessary to understand their characteristics at various temporal and spatial scales. This study aims to examine the characteristics of hydrological droughts and their propagation from meteorological droughts across Wisconsin. Hydrological droughts were identified for twenty-four U.S. Geological Survey streamflow monitoring sites using the 20th percentile threshold level for each calendar day. Meteorological droughts were identified in the same way using daily precipitation data. Drought events of both types were identified for the period from 1980 to 2018, and the drought in 2012 was examined in detail. Our results indicate that (1) unlike meteorological droughts, hydrological droughts tend to occur more frequently in recent years; (2) characteristics of hydrological droughts are not correlated with those of meteorological droughts or annual precipitation; (3) there are generally three drought regions in Wisconsin showing different drought trends and propagation characteristics; and (4) groundwater withdrawal from unconfined aquifers has exacerbated hydrological droughts. In conclusion, hydrological droughts have become less synchronous with meteorological droughts, which will make drought early warning more challenging. The study sheds light on drought characteristics and propagation in relation to catchment characteristics and human activities.